The Biomechanics Laboratory makes available to clinicians and researchers at the NIH quantitative information concerning human motion. The Laboratory has a computer-operated television motion analysis system (VICON) to acquire and evaluate data. The system detects the presence of reflective markers located on the patient and calculates the three dimensional location of each marker. The problems with persistence, blooming, and electronic stability of the vidicon cameras makes the balancing and calibration of the six cameras difficult. Also, problems with video overload are encountered when a strobed infrared (IR) Light Emitting Diode (LED) array is viewed by another camera. The solution is to replace the vidicon cameras with CCD cameras, which have superior electronic stability and do not display-picture smearing when detecting fast motion. Each camera has a strobed IR array to illuminate the field of view. To eliminate the illumination cross-talk between cameras, each IR array is equipped with IR emitters with wavelengths of either 880nm or 950nm. An IR band-pass filter that matches the wavelength of the array is placed over the camera lens.